Something that's been bugging me.

[ChaosK]

they dont go off on there own and teach genin because the jounin are the ones who teach the genin not chuunin

No they both do. Some Genins have Chuunin instructors. I'd imagine not all jounins are babysitters, after all only three teams make it to an actual Genin, in other words, only three instructors for each graduating class are needed. I doubt they'd have to call upon Kakashi, Kurenai or Asuma (now dead) again for a while.

The old instructors now just go on missions in a team as ninjas. For example we've seen time and time again Kakashi being away on a mission.

[Super5]

I'm not sure why the jounin don't take on new students... except that maybe those teams work so well together that Tsunade doesn't want to break them up. Another possibility is that less-experienced Jounin have been taking on the new genin recently.

[Everon]

Eecently we've seen Shikamaru work with other chunnin (granted it was under Sarutobi-Sensei). That's their gentle suggestion that teams often get formed based on needed abilities during a mission.

The eight teams were originally built so that teammates would complement each other's abilities. Along with teamwork experience, it makes sense to use the these configured teams often.